photochemical machining of SS304

International Journal of Advances in Science and Technology, Vol. 3, No.4, 2011

Photochemical Machining of SS304

Atul R. Saraf1 and M. Sadaiah2

1Department of Mechanical Engineering, Dr. Babasaheb Ambedkar Technological University, Lonere, Raigad, Maharashtra State, India

[email protected]

2Department of Mechanical Engineering, Dr. Babasaheb Ambedkar Technological University, Lonere, Raigad, Maharashtra State, India

[email protected]

Abstract

This paper presents the machining of SS304 using Photochemical Machining (PCM).

Twenty-seven experimental runs base on full factorial (33) Design of Experiments (DoE) technique

were performed. The control parameters considered were the etchant concentration, etching

temperature and etching time. The response parameter was Undercut (Uc). The effect of control

parameters on undercut was analyzed using Analysis of Variance (ANOVA) technique and their

optimal conditions were evaluated. The minimum undercut (Uc) was observed at the etching

temperature of 60 c, etching concentration of 600 gm/litre and 30 minutes etching time. It was

found that etchant temperature and etching time are the most significant factors for undercut.

Keywords: PCM, DoE, ANOVA, Undercut.

1. Introduction

The PCM is one of the non-conventional machining processes that produces a burr free and

stress free flat complex metal components. The machining takes place using a controlled dissolution of

work-piece material by contact of the strong chemical solution. The PCM industry currently plays a

vital role in the production of a variety of precision parts viz. microfluidic channels, silicon integrated

circuits, copper printed circuit boards and decorative items. It is mainly used for manufacturing of

micro-components in various fields such as electronics, aerospace and medical. It employs chemical

etching through a photo-resist stencil as a method of material removal over selected areas. This

technique is relatively modern and became established as a manufacturing process. The newly-

developed products made from PCM especially relevant to Micro-engineering, Micro-fluidics and

Microsystems Technology.

International Journal of Advances in Science and Technology

SS 304 is important material for various engineering applications. Its wide usage is due its

high strength, poor thermal conductivity. Copper etching is a main process in production of printed

circuit boards. Historically, first used etchant in printed circuit boards fabrication was ferric chloride

and it is still used as an etchant for small scale industries as a commercial etchant. The most commonly

used etchant is an aqueous solution of ferric chloride (FeCl3). Very less literature is available on the

photochemical machining. Therefore, it seems that PCM is not well understood as other non-

conventional machining techniques like electro discharge machining (EDM), electrochemical

machining (ECM) and laser beam machining (LBM). The PCM industry currently plays a valuable role

worldwide in the production of a very wide range of precision parts, decorative items, copper printed

circuit boards and silicon integrated circuits. In the multi-stage PCM process, the use of photoresists

enables fabrication of high resolution parts with complex, plan view geometry or with large arrays of

variable aperture profiles in thin (< 2mm thick) flat metal sheet and thereby often bestows technical

and economic advantages over:

Traditional metal cutting techniques

Chemical milling used for lower resolution applications over larger areas

Other non-traditional machining techniques such as laser cutting, wire-EDM and stamping.

Cakir (2008) found that FeCl3 as very suitable etchant for aluminum etching. The chemical reaction is

simple, that makes the process easy to control. Cakir (2006) studied that copper etching with CuCl2

etchant and a suitable regeneration process of waste etchant simultaneously. This would make the

overall manufacturing cost low and environmentally friendly etching process. David et al. (2004)

studied Characterization of aqueous ferric chloride etchants used in industrial photochemical

machining. Fecl3 most commonly used as etchants but there is wide variety in grades of Fecl3.

Rajkumar et al. (2004) investigated the cost model for PCM which defines standards for industrial

etchants and methods to analyze and monitor them. David et al. (1983) studied manufacturing of

stainless steel edge filters: an application of electrolytic Photo polishing and stated the two methods for

manufacturing of edge filter. Also the surface textures and process characteristics of the electrolytic

photoetching of annealed AlSl 304 stainless steel in hydrochloric acid was studded. Jonathan et al.


(1995) studied direct printing of etch masks under computer control in which all the stages of photo-

processing and mask making.

It found from past literature, that no statistical study has been reported to analyze the interaction effects

of process parameters on etching process of copper. It depends only on experience of operator and an

optimal set of parameter required for process is not calculated, it is taken only by experience. The study

is necessary to investigate the performance in different ranges, and to find the global optimum

parameters. It is necessary to find out single optimum process parameters setting to satisfy the

requirements of excellent etching quality. In this paper attempt is made to finalize optimum process

parameters by using Full Factorial design method and ANOVA technique.

2. Undercut

Undercut means etching takes place along vertical face of work piece and after etching a bigger slot than that of requirement is produced (Fig. 2). There is a requirement of consideration of undercut.

Fig. 1 Undercut = (B-A).

before etching for getting accurate dimension [1].

3. Design of experiments

In this study, experiments were designed on the basis of the experimental design technique

which refers to the planning of experiments, collection and analysis of data with near-optimum use of

available resource. It is an experimental method designed and developed for evaluating the effects of

process parameters on performance characteristics. It determines the process parameter conditions for

optimum response variables. During experimentation, a large number of experiments have to be carried

out as the number of machining parameters increases. Design of experiments involves proper selection

of variables (input factors) and their interactions. The use of statistically derived full factorial design


gives the number of experimental runs to be carried out without affecting the quality of the analysis.

Therefore, the full factorial design method was used to determine optimal machining parameters for

minimum undercut. The 3k full factorial design consists of all combinations of the k factors taking on

three levels. These are high, medium and low levels of factors. Accordingly to 3k full factorial design,

27 experiments were planned as per the selected design with one replication.

The present investigation studied the results of the effects of Concentration, Time and Temperature on

the undercut during the PCM process of SS304. Input parameters and their levels are shown in Table 1.

Table 1. Design matrix.

Test Temperature(0C) Concentration(gm/liter) Time(minute) 1 1 1 1 2 1 1 2 3 1 1 3 4 1 2 1 5 1 2 2 6 1 2 3 7 1 3 1 8 1 3 2 9 1 3 3 10 2 1 1 11 2 1 2 12 2 1 3 13 2 2 1 14 2 2 2 15 2 2 3 16 2 3 1 17 2 3 2 18 2 3 3 19 3 1 1 20 3 1 2 21 3 1 3 22 3 2 1 23 3 2 2 24 3 2 3 25 3 3 1 26 3 3 2 27 3 3 3


4. Experimental work

In this work, Ferric Chloride (FeCl3) was used as an etchant for machining of OFHC copper. The chemical composition of SS 304 is shown in Table 2. The etchant, FeCl3 was prepared in 500,600, and 700 gm/litre respectively. For each experiment 5000 ml. of etchant was used.

Table 2. Chemical composition of SS304.

Element C Si Mn Cr Mo P S Ni

%age 0.05487 0.510 1.82 18.37 0.210 0.0244 0.01051 7.08

Etchant was poured into etching bath that is coated by insulator jacket to control chemical etching temperature and also partially air tight is shown in Fig. 1. Photochemical machining tests were carried out at 40 C, 50 C and 60 C. The temperature was maintained within a range of 1 C. Single-sided chemical etching process was used. The etching times were 30, 40 and 50 minutes.

Figure 2. Experimental set-up for etching. The DOE technique was used to design the experiments to know the interaction of process parameters. Each parameter was designed to have three levels namely low, medium and high respectively (Number of treatment conditions = 3k = 33 = 27) using a full factorial DoE technique. The experimental design matrix was a simplified method of putting together an experiment (Table 3).

Table 3.Experimental Design matrix.

T.C. Temperature(0C) Concentration(gm/liter)

Time (minute)

1 40 500 30 2 40 500 40 3 40 500 50 4 40 600 30 5 40 600 40 6 40 600 50 7 40 700 30 8 40 700 40 9 40 700 50

10 50 500 30 11 50 500 40 12 50 500 50 13 50 600 30


14 50 600 40 15 50 600 50 16 50 700 30 17 50 700 40 18 50 700 50 19 60 500 30 20 60 500 40 21 60 500 50 22 60 600 30 23 60 600 40 24 60 600 50 25 60 700 30 26 60 700 40 27 60 700 50

5. Results and discussion

The analysis of experimental data was performed in order to determine the effect of temperature, time and concentration on the magnitude of undercut. The analyzed results are presented using main effects and interaction plots.

5.1 Statistical analysis of the undercut (Uc)

The summary of analysis of variance (ANOVA) is shown in Table 4. It is observed that the factor undercut has a significant effect at 95% confidence interval as evident from ANOVA Table 4. It is observed that etching time and etchant temperature has a large contribution on the variability of undercut among the selected parameters. However, the concentration has negligible effect on undercut. The ANOVA for undercut shows that the time and temperature are the most significant parameters for undercut.

Table 4. ANOVA for undercut (mm).

Factors

Degree of

Freedom

Sum of

Square

Mean of

Square

Variance Relation

F

F critical

at =0.05

p- value

Significant (Yes/No)

Temperature(0C) 2 0.0009183 0.0009183 0.0004592 18.48 0.001 Yes Concentration(gm/liter) 2 0.0001770 0.0001770 0.0000885 3.56 0.078 No Time (minute) 2 0.0006159 0.0006159 0.0006159 1.45 0.004 Yes Error 8 0.0001988 0.0001988 0.0001988 Total 26

Etching process if prolonged, undercut was always going to be more, as etching starts in sidewise with downward action also. The evaluation of undercut as a function of temperature, concentration and time is shown in Fig. 2.


605040

0.015

0.010

0.005

700600500

504030

0.015

0.010

0.005

temp

Mean

conc

time

Main Effects Plot for undercutData Means

Figure 3. Main effect plots for undercut Uc (mm). The main effects plots show that the response undercut was increased with increasing in etch time. But initially at lower level undercut was very small and it was very high at higher levels. The parameters that have greater influence on undercut in the decreasing order of importance are time, temperature and and concentration as shown in Fig. 3. The time has the most dominant effect amongst all the main parameters. Further, it is better to set the time at a lower level, concentration, at medium level and temperature at higher level. It is observed from the main effects plots (Fig. 3) that the optimum etching performance parameters for the undercut were observed at a temperature of 60 c, a concentration of 600 gm/litre and etching time of 30 minutes. Fig. 4 shows the interaction plot for undercuts, with each plot exhibits the interaction between two different machining parameters.

0.030

0.015

0.000

504030

700600500

0.030

0.015

0.000

605040

0.030

0.015

0.000

temp

conc

time

40

50

60

temp

500

600

700

conc

30

40

50

time

Interaction Plot (data means) for undercut

Figure 4. Interaction plots for undercut Uc (mm).

6. Conclusions

From the experimental investigations based on full factorial method and the analysis of the results, the following conclusions are drawn.

It is observed from the ANOVA, the input variables time and temperature both have statistically significant effects on the undercut.


The above discussion confirmed the validity of the full factorial methodology for enhancing the etching performance and optimizing the etching parameters. The undercut is greatly improved by this approach.

For minimum Undercut (Uc), the temperature was 60 c, etchant concentration 600 gm/litre and etching time 30 minutes.

.

References

[1] David M. A., 2004, Photochemical Machining: From Manufacturings Best Kept secret to a $6 Billion per annum, Rapid Manufacturing Process, CIRP Journal of Manufacturing Systems, 53, 559-573.

[2] O. Cakr, 2008, Chemical etching of aluminum, journal of materials processing technology, 199,3373400.

[3] O. Cakr, 2006, Copper etching with cupric chloride and regeneration of waste etchant, journal of materials processing technology, 175, 6368.

[4] David M. A., Heather, J.A. Heather J.A., 2004, Characterization of aqueous ferric chloride etchants used in industrial photochemical machining, Journal of Materials Processing Technology, 149, 238245.

[5] David, M. A., Talib, T.N., 1983, Manufacture of stainless steel edge filters: an application of electrolytic photopolishing, precision engineering, 57-59.

[6] David M. A., Talib, T.N., 1983, Surface textures and process characteristics of the electrolytic photoetching of annealed AlSl 304 stainless steel in hydrochloric acid precision engineering.

[7] Davis, P.J., Overturf, G.E., 1986, Chemical machining as a precision material removal process, precision engineering , 67-71.

[8] Douglas, C. M.,1997, Design and Analysis of Experiments. Fifth Edition, John wiley and sons, INC.

[9] Jonathan, M.,George, M. A.,1995, Direct printing of etch masks under computer control, Int. J. Mach. Tools Manufacture.Vol.35, No.2, 333-337.

[10] Rajkumar, R., Heather J.A., Oscar Zamora., 2004, Cost of photochemical machining, Journal of Materials Processing Technology, 149, 460465.

[11] Atul R.Saraf, M.Sadaiah, 2011, Optimization of Photochemical Machining, International journal of Engineering Science and Technology (IJEST)


Authors Profile

Dr. M. Sadaiah received his M.E. from University College of Engineering/Osmania University, Hyderabad ,India in 1990 and Ph.D degree from PSG College of Technology, Coimbatore/Bharatiyar University, Coimbatore, India in 2003. He is currently working as a Assistant professor in Department of Mechanical Engineering, Dr. Babasaheb Ambedkar Technological University. He is having overall teaching experience of 19 years. His major research interests are Feature Extraction, CAPP, CAD/CAM/CIM, Micromachining, Machining of Advanced Materials, Tool Condition Monitoring/Nano-technology and Photochemical Machining. A life member of Indian Society for Technical Education, Indian Society of Mechanical Engineers.

Mr. Atul R. Saraf received his M.Tech degree from Dr. Babasaheb Ambedkar Technological University, India in 2011. He is having overall industrial experience of 2 years. His major research Interests are in Fuzzy logic, Artificial Intelligence and Advanced Machining Processes, Mfg Process Selection and Mfg Process Parameters Optimization and Photochemical Machining.

photochemical machining of SS304

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